This proposal is designed to provide the candidate a period of mentored research in the laboratory of Dr. A. T. Look, a pioneer in the field of zebrafish neoplasias and myeloid development. Dr. Look's clinical and research expertise, collaborations, and resources will assist the candidate in developing the skills and autonomy required to become a successful independent investigator. In addition, an advisory committee of highly regarded scientists will provide scientific and career advice. The goal of this application is to use the zebrafish as a model to study novel genes and pathways necessary for myeloid development that can subsequently be examined for similar roles in mammalian systems. Mammalian hematopoiesis is a multistep process involving the progressive commitment of pluripotent hematopoietic stem cells into the wide variety of terminally differentiated cells of the blood system. The successive waves of tissue specification are regulated by specific patterns of gene expression. In zebrafish, most mature blood cell types and key transcription factors are conserved, suggesting that the regulatory mechanisms directing lineage specification are similarly conserved. To identify novel genes involved in myeloid development, the candidate has analyzed a panel of zebrafish insertional mutants, provided by Dr. Nancy Hopkins at MIT, and identified mutants with deficient or abnormal distribution of myeloperoxidase, a gene specifically expressed in zebrafish granulocytes. This proposal will focus on mutants of the transcription factor supt6h, ubiquitin ligase F-Box 5 (fbxo5), Na/K ATPase (atp1a1), or Replication Protein A (rpa1) genes. The central hypothesis of this work is that these genes will have critical roles in normal myeloid development. To address this hypothesis, the hematopoietic phenotypes of the mutants will be analyzed and the role of individual genes in myeloid development will be examined. The analysis of these mutants will establish the basis for future studies in myeloid development and malignancies by this candidate.